[FFmpeg-devel] [PATCH 2/2] libavcodec/v4l2: use libdrm
Scott Theisen
scott.the.elm at gmail.com
Wed Dec 18 06:23:17 EET 2024
On 12/17/24 11:10, Zhao Zhili wrote:
>> On Dec 17, 2024, at 06:48, Scott Theisen <scott.the.elm at gmail.com> wrote:
>>
>> On 12/15/24 22:15, Zhao Zhili wrote:
>>>> On Dec 15, 2024, at 12:14, Scott Theisen<scott.the.elm at gmail.com> wrote:
>>>>
>>>> Based on patches by Lukas Rusak from
>>>> https://github.com/lrusak/FFmpeg/commits/v4l2-drmprime-v4
>>>>
>>>> libavcodec: v4l2m2m: output AVDRMFrameDescriptor
>>>> https://github.com/lrusak/FFmpeg/commit/2cb8052ac65a56d8a3f347a1e6f12d4449a5a614
>>>>
>>>> libavcodec: v4l2m2m: depends on libdrm
>>>> https://github.com/lrusak/FFmpeg/commit/ab4cf3e6fb37cffdebccca52e36a7b2deb7e729f
>>>>
>>>> libavcodec: v4l2m2m: set format_modifier to DRM_FORMAT_MOD_LINEAR
>>>> https://github.com/lrusak/FFmpeg/commit/9438a6efa29c7c7ec80c39c9b013b9a12d7b5f33
>>>>
>>>> libavcodec: v4l2m2m: only mmap the buffer when it is output type and drm prime is used
>>>> https://github.com/lrusak/FFmpeg/commit/093656607863e47630de2d1cfcf0ac8e4b93a69e
>>>>
>>>> libavcodec: v4l2m2m: allow using software pixel formats
>>>> https://github.com/lrusak/FFmpeg/commit/8405b573e83838e6b2fea99825fbef32ee9f7767
>>>>
>>>> libavcodec: v4l2m2m: implement hwcontext
>>>> https://github.com/lrusak/FFmpeg/commit/b2c1f1eb39b54bf034497a7f2a7f23855d0a7cde
>>>>
>>>> libavcodec: v4l2m2m: implement flush
>>>> https://github.com/lrusak/FFmpeg/commit/e793ef82727d6d6f55c40844463d476e7e84efad
>>>>
>>>> Originally added to MythTV in:
>>>> FFmpeg: Patch FFmpeg for V4L2 codecs DRM PRIME support
>>>> https://github.com/MythTV/mythtv/commit/cc7572f9b26189ad5d5d504c05f08e53e4e61b54
>>>>
>>>> FFmpeg: Re-apply v4l2 memory to memory DRM_PRIME support
>>>> https://github.com/MythTV/mythtv/commit/1c942720591b5b7820abe9ed0d805afabbdffe3c
>>>>
>>>> modified in:
>>>> V4L2 Codecs: Fix lockup when seeking
>>>> https://github.com/MythTV/mythtv/commit/fdc0645aba9a9ad373888bd62ebcbc83a3feb7e5
>>>>
>>>> v4l2_buffers: Add some libdrm ifdef's
>>>> https://github.com/MythTV/mythtv/commit/336df1067abfa4fe7cf611541e5b6f3561fc81a2
>>>>
>>>> !!!!
>>>> NB: libavcodec/v4l2_m2m_dec.c: v4l2_decode_init(): I'm returning -1
>>>> since I don't know what error code I should use.
>>>>
>>>> Note also Lucas Rusak's v5 series:
>>>> closer diff to current state, otherwise unchanged
>>>> libavcodec: v4l2m2m: output AVDRMFrameDescriptor
>>>> https://github.com/lrusak/FFmpeg/commit/c6b85ed30f06ea99513b13cc768a922ebe4d68c2
>>>>
>>>> new option:
>>>> libavcodec: v4l2m2m: add option to specify pixel format used by the decoder
>>>> https://github.com/lrusak/FFmpeg/commit/ffc4419f456c00ab71cf93f792b0473c6de14e64
>>>>
>>>> additional code vs v4
>>>> libavcodec: v4l2m2m: implement flush
>>>> https://github.com/lrusak/FFmpeg/commit/8595d06d4909bbec0aa14625fcfc869c6bcef696
>>>> ---
>>>> configure | 1 +
>>>> libavcodec/v4l2_buffers.c | 206 +++++++++++++++++++++++++++++++++++---
>>>> libavcodec/v4l2_buffers.h | 4 +
>>>> libavcodec/v4l2_context.c | 43 +++++++-
>>>> libavcodec/v4l2_context.h | 2 +
>>>> libavcodec/v4l2_m2m.h | 5 +
>>>> libavcodec/v4l2_m2m_dec.c | 62 ++++++++++++
>>>> 7 files changed, 305 insertions(+), 18 deletions(-)
>>>>
>>>> diff --git a/configure b/configure
>>>> index bf55ba67fa..5f02cf3b51 100755
>>>> --- a/configure
>>>> +++ b/configure
>>>> @@ -3770,6 +3770,7 @@ sndio_indev_deps="sndio"
>>>> sndio_outdev_deps="sndio"
>>>> v4l2_indev_deps_any="linux_videodev2_h sys_videoio_h"
>>>> v4l2_indev_suggest="libv4l2"
>>>> +v4l2_outdev_deps="libdrm"
>>> Why v4l2_outdev when the patch is for libavcodec?
>> Lukas Rusak appears to have only submitted up to v3 of his patches in 2018.
>>
>> This appears to be from a comment in https://patchwork.ffmpeg.org/project/ffmpeg/patch/4bbeff66-6123-9296-5775-96d75809eee0@jkqxz.net/
>>
>> However, with the `#if CONFIG_LIBDRM`s added by Mark Kendall for MythTV, I don't think it is a hard dependency.
>>
>> ...
>>>> diff --git a/libavcodec/v4l2_m2m_dec.c b/libavcodec/v4l2_m2m_dec.c
>>>> index aa2d759e1e..cfeee7f2fb 100644
>>>> --- a/libavcodec/v4l2_m2m_dec.c
>>>> +++ b/libavcodec/v4l2_m2m_dec.c
>>>> @@ -23,12 +23,17 @@
>>>>
>>>> #include <linux/videodev2.h>
>>>> #include <sys/ioctl.h>
>>>> +
>>>> +#include "libavutil/hwcontext.h"
>>>> +#include "libavutil/hwcontext_drm.h"
>>>> #include "libavutil/pixfmt.h"
>>>> #include "libavutil/pixdesc.h"
>>>> #include "libavutil/opt.h"
>>>> #include "libavcodec/avcodec.h"
>>>> #include "codec_internal.h"
>>>> #include "libavcodec/decode.h"
>>>> +#include "libavcodec/internal.h"
>>>> +#include "libavcodec/hwconfig.h"
>>>>
>>>> #include "v4l2_context.h"
>>>> #include "v4l2_m2m.h"
>>>> @@ -205,7 +210,44 @@ static av_cold int v4l2_decode_init(AVCodecContext *avctx)
>>>> capture->av_codec_id = AV_CODEC_ID_RAWVIDEO;
>>>> capture->av_pix_fmt = avctx->pix_fmt;
>>>>
>>>> + /* the client requests the codec to generate DRM frames:
>>>> + * - data[0] will therefore point to the returned AVDRMFrameDescriptor
>>>> + * check the ff_v4l2_buffer_to_avframe conversion function.
>>>> + * - the DRM frame format is passed in the DRM frame descriptor layer.
>>>> + * check the v4l2_get_drm_frame function.
>>>> + */
>>>> + {
>>>> + const enum AVPixelFormat *pix_fmts = NULL;
>>>> + int num_pix_fmts = 0;
>>>> + ret = avcodec_get_supported_config(avctx, NULL, AV_CODEC_CONFIG_PIX_FORMAT,
>>>> + 0, (const void **) &pix_fmts, &num_pix_fmts);
>>> I don’t think here is the meant use case for avcodec_get_supported_config.
>>> Specify available pixel format directly in pix_fmts.
>>>
>>>> + if (ret < 0)
>>>> + return ret;
>>>> + if (pix_fmts == NULL || num_pix_fmts < 1)
>>>> + return -1;
>>> There is no which error code to use issue after remove avcodec_get_supported_config.
>>>
>> AVCodec::pix_fmts was deprecated, so I replaced it with avcodec_get_supported_config() in
>> https://github.com/ulmus-scott/FFmpeg/commit/7ac4b4fc2282b4fdda78ffb1a446ceb85b681661
>>
>> Was that incorrect?
> Firstly, AVCodec::pix_fmts was deprecated, which should be replaced by FFCodec::get_supported_config
> callback for **internal implementation**. avcodec_get_supported_config is towards for libavcodec API users.
I don't see any problem with calling the public API internally.
> Secondly, AVCodec::pix_fmts and FFCodec::get_supported_config is for **encoder**. For decoder, it’s
> AVCodecContext::get_format callback to do the negotiate, for example, h264_slice.c get_pixel_format().
OK, the list would only conditionally contain AV_PIX_FMT_DRM_PRIME then?
>
>>>> + switch (ff_get_format(avctx, pix_fmts)) {
>>>> + case AV_PIX_FMT_DRM_PRIME:
>>>> + s->output_drm = 1;
>>>> + break;
>>>> + case AV_PIX_FMT_NONE:
>>>> + return 0;
>>>> + break;
>>> Why return 0 for AV_PIX_FMT_NONE? It’s suspicious.
>>> ‘break’ can be removed.
>> That is from https://github.com/lrusak/FFmpeg/commit/8405b573e83838e6b2fea99825fbef32ee9f7767
>>
>> I agree return 0 is strange. All I can say is that is what the code used by MythTV is and has been for years. (Maybe MythTV always requests AV_PIX_FMT_DRM_PRIME?)
>>
>> This change is not used by MythTV but maybe https://github.com/lrusak/FFmpeg/commit/ffc4419f456c00ab71cf93f792b0473c6de14e64 is related or an alternate way of requesting the pixel format?
>>
>>>> + default:
>>>> + break;
>>>> + }
>>>> + }
As the change currently stands, I think this is equivalent to
`s->output_drm = 1;`.
>>>> +
>>>> + s->device_ref = av_hwdevice_ctx_alloc(AV_HWDEVICE_TYPE_DRM);
>>>> + if (!s->device_ref) {
>>>> + ret = AVERROR(ENOMEM);
>>>> + return ret;
>>>> + }
>>> I’m not sure whether there is use case to let user specify device?
>> This is from https://github.com/lrusak/FFmpeg/commit/b2c1f1eb39b54bf034497a7f2a7f23855d0a7cde
>>
>> I don't know what you mean by "let user specify device".
> User can create a DRM hw device directly via hwcontext API, and provided to decoder via
> AVCodecContext::hw_device_ctx. It don’t looks right to always create hw device directly inside
> the decoder implementation.
rkmppdec.c always creates its own hardware device context.
>
>>>> +
>>>> s->avctx = avctx;
>>>> + ret = av_hwdevice_ctx_init(s->device_ref);
>>>> + if (ret < 0)
>>>> + return ret;
>>>> +
>>>> ret = ff_v4l2_m2m_codec_init(priv);
>>>> if (ret) {
>>>> av_log(avctx, AV_LOG_ERROR, "can't configure decoder\n");
So are you saying this should require the user to create the hardware
context before calling avcodec_open2()? And the change would then be
something like this:
```
s->output_drm = 0;
#if CONFIG_LIBDRM
if (avctx->hw_device_ctx != NULL &&
((AVHWDeviceContext*)avctx->hw_device_ctx->data)->type ==
AV_HWDEVICE_TYPE_DRM)
s->output_drm = 1;
#endif
```
What about AVCodecContext::hw_frames_ctx?
>>>> @@ -220,6 +262,16 @@ static av_cold int v4l2_decode_close(AVCodecContext *avctx)
>>>> return ff_v4l2_m2m_codec_end(avctx->priv_data);
>>>> }
>>>>
>>>> +static void v4l2_flush(AVCodecContext *avctx)
>>>> +{
>>>> + V4L2m2mPriv *priv = avctx->priv_data;
>>>> + V4L2m2mContext* s = priv->context;
>>>> +
>>>> + /* wait for pending buffer references */
>>>> + if (atomic_load(&s->refcount))
>>>> + while(sem_wait(&s->refsync) == -1 && errno == EINTR);
>>>> +}
>>> Does refcount depends on users behavior like holding a frame? Is it possible to run into deadlock here, e.g.,
>>> user request flush while holding some frames?
>> I don't know, but Lukas Rusak removed that in his v5 patch (not used by MythTV) https://github.com/lrusak/FFmpeg/commit/8595d06d4909bbec0aa14625fcfc869c6bcef696
>>
>> Original v4 patch for reference: https://github.com/lrusak/FFmpeg/commit/e793ef82727d6d6f55c40844463d476e7e84efad
>>
>>>> +
>>>> #define OFFSET(x) offsetof(V4L2m2mPriv, x)
>>>> #define FLAGS AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
>>>>
>>>> @@ -230,6 +282,11 @@ static const AVOption options[] = {
>>>> { NULL},
>>>> };
>>>>
>>>> +static const AVCodecHWConfigInternal *v4l2_m2m_hw_configs[] = {
>>>> + HW_CONFIG_INTERNAL(DRM_PRIME),
>>> Depends on whether allow user to specify drm device.
>> This is from the main patch https://github.com/lrusak/FFmpeg/commit/2cb8052ac65a56d8a3f347a1e6f12d4449a5a614
>>
>> Unless this is used internally by FFmpeg, MythTV does not appear to use it.
>>
Regards,
Scott Theisen
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